Airborne bacterial, viral and fungal cells and spores may be present in the air as bioaerosols (in droplets), which are very small individual particles that stay suspended in air for long periods or may aggregate as larger clumps that settle rapidly onto surfaces. It is desirable to identify airborne pathogens, for example to prevent an outbreak of diseases. However, detecting airborne pathogens is challenging due to the comparably low density of pathogens in the air.
There are generally two principle ways of monitoring the microbiological population of the air, passive monitoring and active sampling. Passive monitoring is usually done using so called settle plates, which are often standard Petri dishes containing appropriate culture media. These are opened and exposed to the air for a predetermined time and then incubated to allow visible colonies to develop and be counted. The active air sampling, in contrast, comprises an active enrichment step. Thereby, a known volume of air is physically drawn on or through a particle collection device, the so called air sampler.
There are different types of air samplers. For example, two very common and most commercially available types of air samplers are, the so called impingers, which use a liquid medium for particle collection, and the so called impactor samplers, which use a solid or adhesive medium, such as standard agar plates, for particle collection. For example, a laminar air flow can be directed onto the collection surface of an impactor.
Another method of active air sampling is filtering the sample, whereby air is drawn by a pump or other vacuum device through a membrane filter. An advantageous kind of membrane filters for this purpose are gelatin membrane filters. Due to the possibility to dissolve the gelatin filters, microorganisms can be recovered and transferred to a detection assay. Gelatin membrane filters are usually used in stationary air samplers. One kind of air sampler known by the applicant is configured for air monitoring and constructed as a stationary system. Other kinds of air samplers known by the applicant include a battery, a vacuum pump, a control panel and a filter head together in one housing and are configured portable.